<html>
 <head>
  <link href="./leetcode-problem.css" rel="stylesheet" type="text/css">
 </head>
 <body>
  <div class="question_difficulty">
   难度：Easy
  </div>
  <div>
   <h1 class="question_title">
    125. Valid Palindrome
   </h1>
   <p>
    Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.
   </p>
   <p>
    <strong>
     Note:
    </strong>
    &nbsp;For the purpose of this problem, we define empty string as valid palindrome.
   </p>
   <p>
    <strong>
     Example 1:
    </strong>
   </p>
   <pre>
<strong>Input:</strong> "A man, a plan, a canal: Panama"
<strong>Output:</strong> true
</pre>
   <p>
    <strong>
     Example 2:
    </strong>
   </p>
   <pre>
<strong>Input:</strong> "race a car"
<strong>Output:</strong> false
</pre>
  </div>
  <div>
   <h1 class="question_title">
    125. 验证回文串
   </h1>
   <p>
    给定一个字符串，验证它是否是回文串，只考虑字母和数字字符，可以忽略字母的大小写。
   </p>
   <p>
    <strong>
     说明：
    </strong>
    本题中，我们将空字符串定义为有效的回文串。
   </p>
   <p>
    <strong>
     示例 1:
    </strong>
   </p>
   <pre><strong>输入:</strong> "A man, a plan, a canal: Panama"
<strong>输出:</strong> true
</pre>
   <p>
    <strong>
     示例 2:
    </strong>
   </p>
   <pre><strong>输入:</strong> "race a car"
<strong>输出:</strong> false
</pre>
  </div>
 </body>
</html>